Conventional roadbeds mainly include a rockfill roadbed, a soil-filled roadbed, and a rock-soil filled roadbed, the latter being the most common roadbed. The rock-soil filled roadbed needs to be filled by soil and rocks acquired from a borrow pit. There is a relatively large difference in physical and mechanical properties of fillers in different areas because of complex geological conditions in a highway construction site. If multiple types of soil-rock mixtures with different physical and mechanical properties are laid on the same pavement layer of a roadbed, it is difficult to compact and level the roadbed. Therefore, differential settlement can occur extremely easily after construction, thereby resulting in destruction and deformation of the road surface.
Phosphogypsum is a by-product produced when a wet process is adopted to produce phosphoric acid in a chemical plant by reaction between apatite and sulfuric acid. For every 1 ton of phosphoric acid produced, approximately 5 tons of phosphogypsum is produced. Phosphogypsum is a powdery material with almost no plasticity. There is phosphoric acid, sulfuric acid, and hydrofluoric acid in phosphogypsum, and therefore phosphogypsum is slightly acidic. More than 8 million tons of phosphogypsum is produced every year in China. By the end of 2011, more than 300 million tons of phosphogypsum in total has accumulated in China. If specific technical measures can be taken to apply phosphogypsum to roadbed filling, phosphogypsum stockpiling will be greatly reduced. On one hand, land resources are saved, and geological disasters of a phosphogypsum dam can be avoided. On the other hand, the problem of highway roadbed filling in a soil-deficient area can be resolved.